eal: fix missing header dependency

rte_pci.h depends upon stdio.h for the definition of the FILE type. Add
in #include <stdio.h> to the file to satisfy this dependency in cases
where the including C file does not already include stdio.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Marc Sune <marc.sune@bisdn.de>